Abstract

We present a new, fast algorithm for rendering physically-based soft
shadows in ray tracing-based renderers. Our method replaces the
hundreds of shadow rays commonly used in stochastic ray tracers
with a single shadow ray and a local reconstruction of the visibility
function. Compared to tracing the shadow rays, our algorithm produces
exactly the same image while executing one to two orders of
magnitude faster in the test scenes used. Our first contribution is a
two-stage method for quickly determining the silhouette edges that
overlap an area light source, as seen from the point to be shaded.
Secondly, we show that these partial silhouettes of occluders, along
with a single shadow ray, are sufficient for reconstructing the visibility
function between the point and the light source.